In the oil and gas industry, seismic prospecting techniques commonly are used to aid in the search for and evaluation of subterranean hydrocarbon deposits. A seismic prospecting operation typically proceeds in three separate stages: data acquisition, data processing, and data interpretation. Success of the prospecting operation often depends on satisfactory completion of all three stages.
In the data acquisition stage, a seismic source emits an acoustic impulse known as a seismic signal that propagates into the earth and is at least partially reflected by subsurface seismic reflectors (i.e., interfaces between underground formations having different acoustic impedances). The reflected signals (known as seismic reflections) are detected and recorded by an array of seismic receivers located at or near the surface of the earth, in an overlying body of water, or at known depths in boreholes.
During the data processing stage, raw seismic data recorded in the data acquisition stage are refined and enhanced using a variety of procedures that depend on the nature of the geologic structure being investigated and on characteristics of the raw data. In general, the purpose of the data processing stage is to produce an image of the subsurface from the recorded seismic data for use during the data interpretation stage. The image is developed using theoretical and empirical models of the manner in which the seismic signals are transmitted into the earth, attenuated by subsurface strata, and reflected from geologic structures.
The purpose of the data interpretation stage is to determine information about the subsurface geology of the earth from the processed seismic data. The results of the data interpretation stage may be used to determine the general geologic structure of a subsurface region, to locate potential hydrocarbon reservoirs, to guide the development of an already discovered reservoir, or to help manage hydrocarbon extraction operations.
Often, three-dimensional seismic data are a useful tool for seismic prospecting operations. As used herein, a three-dimensional seismic data volume is a three-dimensional volume of discrete x-y-z or x-y-t data points, where x and y are mutually orthogonal, horizontal directions, z is the vertical direction, and t is two-way vertical seismic signal travel time. In subsurface models, these discrete data points are often represented by a set of contiguous hexahedrons known as samples, cells or voxels, with each voxel representing a volume surrounding a single data point. Each data point, cell, or voxel in a three-dimensional seismic data volume typically has an assigned value (data sample) of a specific seismic data attribute such as seismic amplitude, acoustic impedance, or any other seismic data attribute that can be defined on a point-by-point basis. One column of such a volume is often called a seismic data trace or simply a trace, while a slice through such a volume is often called cross section, or simply section.
An interpreter analyzes the seismic data, for example by picking horizons, faults, or other surfaces. The interpreter may also pick polylines or geobodies (three-dimensional sets of connected samples). Polylines, surfaces, and geobodies are examples of interpretation objects, or simply interpretations or objects. The interpreter may perform these picking tasks in a manual manner or in an assisted or automated manner. Especially when using an automated technique, it is possible to generate a large number of interpretations in a relatively short time.
For example, Imhof et al. disclosed an algorithm that extracts essentially every event from a seismic dataset and assigns these events to surfaces (U.S. Patent Application Publication 2011/0048731, “Seismic Horizon Skeletonization”). Other methods for generating a large set of surfaces include U.S. Pat. No. 7,248,539, “Extrema Classification,” to Borgos; U.S. Pat. No. 5,570,106, “Method and Apparatus for Creating Horizons from 3-D Seismic Data,” to Viswanathan; and U.S. Patent Application Publication 2008/0285384, “System and Method for Displaying Seismic Horizons with Attributes,” by James.